Structure-Function Studies on CAR The primary goal of this project is to determine the mechanisms of action of the constitutive androstane receptor (CAR). CAR plays key roles in the clearance of xenobiotics and endogenous toxins such as bilirubin. CAR belongs to the nuclear receptor family of transcription factor proteins that mediate endocrine function and play critical roles in development and physiology and pharmacology. The functional activity of nuclear receptors is regulated by small molecular hormonal and synthetic molecules. CAR is regulated by small-molecule signals. Earlier, we produced preliminary evidence utilizing multiple biophysical and cell-based assays to show how distinct allosteric pathways can fine-tune the activity of nuclear receptors. Our goal here is to identify and distinguish between the different allosteric pathways initiated by ligands, DNA and cofactors such as co- activators and co-repressors. We will use a combination of crystallography and biophysical techniques to determine the local and distant conformational changes that occur upon ligand binding. With Dr. Tongye Shen we will use theoretical techniques to predict allosteric pathways that can be further characterized by experimental techniques. We will also use genomic approaches in colla boration with Dr. Rachel Patton McCord to determine the role of allostery, in vivo. The ultimate goal of this study is to develop our understanding of CAR and nuclear receptors. Malfunctioning nuclear receptors are associated with several disease states, and CAR activity has been associated with the development of liver tumors in mouse models. In summary, we will address the following questions: (i) What conformational pathways link ligand, DNA and coregulatory molecules? (ii) How do these pathways regulate coactivator and DNA recognition? (iii) What is the genome-scale impact of allostery in CAR? Thus, a detailed understanding of these proteins, and CAR, will enable us to develop efficient therapies in the long term.